1. Field of the Invention
The present invention relates to a capacitor for a semiconductor device and, more particularly, to a capacitor for a Dynamic Random Access Memory (DRAM) type semiconductor memory device that is able to effectively increase its capacitance and simplify its manufacturing process.
2. Discussion of the Related Art
There are generally two kinds of capacitor types for a semiconductor device: a stacked capacitor type and a trench capacitor type. The stacked capacitor type is divided into, e.g., a fin type structure, a cylindrical type structure, a box type structure, and other type structures.
A stacked capacitor type having a cylindrical type structure has a storage node electrode forming a cylindrical structure. In order to obtain sufficient cell capacitance, the cylindrical structure has been known to be most suitable for a semiconductor memory device having a 64 Mb or higher memory capacity.
Depending on the number of cylindrical structures and their types, a capacitor of a cylindrical type structure is divided into, e.g., a 1.0 cylinder-type capacitor, a 1.5 cylinder-type capacitor, a 2.0 cylinder-type capacitor, and a higher number cylinder-type capacitor.
Such cylinder-type capacitors have the following disadvantages.
First, a 1.0 cylinder-type capacitor has only one cylinder, which places restrictions on having an increased surface area. This is disadvantageous in providing accumulative capacitance for a cylinder-type capacitor. Second, in the case of a 2.0 cylinder-type capacitor, two cylinders are used, requiring more processing steps. This reduces high production yield and complicates the overall manufacturing process. Third, in the case of a 1.5 cylinder-type capacitor, it is difficult to control a profile of the cylinder-type capacitor using an etching process.
A conventional method for manufacturing a capacitor for a semiconductor device will be described with reference to the accompanying drawings.
Referring to FIGS. 1a through 1d, a conventional method for manufacturing a capacitor for a semiconductor device is illustrated.
First, an insulating material, e.g., an oxide layer, is deposited on a silicon substrate 10 having impurity diffusion regions (not shown) formed therein and cell transistors (not shown) formed thereon, thereby forming a first insulating layer 11, as shown in FIG. 1a. Next, a silicon nitride layer 12 is formed on the first insulating layer 11, and subsequently a photoresist layer (P/R) is deposited and patterned on the silicon nitride layer 12. With the patterned photoresist layer (P/R), which serves as a mask, the silicon nitride layer 12 and the first insulating layer 11 thereunder are selectively removed to form storage node contact holes 13.
As illustrated in FIG. 1b, a first polysilicon layer, which forms first storage node electrodes 14, is formed in the storage node contact holes 13 and on portions of the silicon nitride layer 12. An oxide layer is deposited on the first polysilicon layer by a chemical vapor deposition (CVD) method, so as to form a second insulating layer 15. Then, a photoresist (P/Rxe2x80x2) layer is deposited and patterned on the second insulating layer 15. With the photoresist pattern serving as a mask, the second insulating layer 15 and the first polysilicon layer are selectively removed, thereby forming the first storage node electrodes 14.
Subsequently, as shown in FIG. 1c, a second polysilicon layer, which forms second storage node electrodes 16, is formed on the remaining second insulating layer 15 and on portions of the silicon nitride layer 12. Then, the second polysilicon layer is subjected to etch back to form the second storage node electrodes 16 on the sides of the second insulating layer 15.
Referring to FIG. 1d, the second insulating layer 15, which is surrounded by the first and second storage node electrodes 14 and 16, is removed using a wet-etching process, thereby forming the first and second storage node electrodes 14 and 16 of a capacitor. Even though not shown in the figures, in the following step, a dielectric layer and an upper electrode are deposited on the upper portions of the first and second storage node electrodes 14 and 16, thereby completing the capacitor (having a 1.0 cylindrical type structure).
Referring to FIGS. 2a through 2f, another conventional method for manufacturing a capacitor of a semiconductor device is illustrated.
First, as shown in FIG. 2a, an insulating material, e.g. an oxide layer, is deposited on a silicon substrate 17 having impurity diffusion regions (not shown) formed therein and cell transistors (not shown) formed thereon, thereby forming a first insulating layer 18. Next, a photoresist layer (not shown) is deposited and patterned on the first insulating layer 18.
Then, using the patterned photoresist layer as a mask, the first insulating layer 18 is selectively removed to form a storage node contact hole 24. Thereafter, a first polysilicon layer 19 is formed on the entire surface of the first insulating layer 18 to a thickness that fills the storage node contact hole 24. An oxide layer is deposited on the first polysilicon layer 19 by using a CVD method, so as to form a second insulating layer 20.
Subsequently, a photoresist layer (P/R) is deposited and patterned on the entire surface of the second insulating layer 20. With the patterned photoresist layer, which serves as a mask, the second insulating layer 20 is selectively removed.
Referring to FIG. 2b, a second polysilicon layer 21 is formed on the entire surface of the first polysilicon layer 19 inclusive of the second insulating layer 20.
Referring to FIG. 2c, a third insulating layer 22 is formed on the second polysilicon layer 21.
Referring to FIG. 2d, insulating sidewalls 23 are formed on the sides of the second polysilicon layer 21 by subjecting the third insulating layer 22 to etch back. Thus, portions of the third insulating layer 22 become the insulating sidewalls 23.
Referring to FIG. 2e, using the second insulating layer 20 and the insulating sidewalls 23 as masks, the first and second polysilicon layers 19 and 21 are selectively etched. At this time, since the first polysilicon layer 19 is thicker than the second polysilicon layer 21, as shown in FIGS. 2b and 2c, during the etching process the second polysilicon layer 21 on the second insulating layer 20 is etched to expose the second insulating layer 20. Also, the first polysilicon layer 19 not corresponding to the second insulating layer 20 and insulating sidewalls 23 is selectively removed to have a predetermined thickness.
Finally, as seen in FIG. 2f, the remaining second insulating layer 20 and the insulating sidewalls 23 are completely removed, thus forming a storage node electrode of a capacitor (having a 1.5 cylinder-type structure with a protruding part in a center portion).
Even though not shown in the figures, in the following processing step, a dielectric layer and an upper electrode are deposited on the storage node electrode, thereby completing the capacitor.
In a conventional method for manufacturing a capacitor for a semiconductor device, capacitance is increased by increasing the height of the cylinder pillar of a cylindrical structure, which increases the surface area of the lower electrode. This is accomplished by increasing the height of an oxide layer and the height of a polysilicon layer. But this method is limited because of disadvantages in planarization.
Further, variation in the forms of cylinders may be one method for increasing capacitance. However, this method is difficult in obtaining the process tolerance for keeping up with the higher integration trend. This results in a low efficiency.
Accordingly, the present invention is directed to a capacitor for a semiconductor device that effectively increases capacitance and simplifies its manufacturing process for substantially obviating one or more problems due to limitations and disadvantages of the related art.
An object of the invention is to provide a capacitor for a semiconductor device which is advantageous in obtaining manufacturing process tolerance and planarization for the device and effectively increasing its capacitance.
To achieve these and other advantages and in accordance with the purposes of the present invention, as embodied and broadly described, the capacitor for a DRAM type semiconductor device includes a storage node electrode structure for a capacitor of a semiconductor device having impurity regions formed therein, including a buried layer disposed in a hole of the semiconductor device, the buried layer being in contact with at least one impurity region; a bottom layer formed on the buried layer and extending beyond the buried layer; a first cylindrical electrode having first walls upwardly extending from the bottom layer; and second cylindrical electrodes having second walls upwardly extending from the bottom layer and disposed on outer sides of the first cylindrical electrode Furthermore, the present invention is directed to a semiconductor device having a capacitor formed therein, including a substrate having impurity regions formed therein; an insulating layer disposed on the substrate; a buried layer disposed in a storage node area defined by at least the insulating layer, wherein the buried layer is in contact with at least one of the impurity regions; a bottom layer formed on the buried layer and extending beyond the buried layer; a first cylindrical electrode having first walls upwardly extending from the bottom layer; second cylindrical electrodes having second walls upwardly extending from the bottom layer and disposed on outer sides of the first cylindrical electrode; a dielectric layer disposed on the first cylindrical electrode and the second cylindrical electrodes; and an upper electrode disposed on the dielectric layer.
Moreover, the present invention is directed to a method for manufacturing a capacitor, including the steps of forming a hole in an insulating layer formed on a substrate to expose an impurity region; forming a first conductive layer on the insulating layer; forming an insulating layer pattern on the first conductive layer and selectively removing the insulating layer pattern and first conductive layer; forming a second conductive layer on the first conductive layer; removing anisotropically portions of the second conductive layer; removing the insulating layer pattern; forming a dielectric layer on the second conductive layer; and forming a third conductive layer on the dielectric layer.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.